Sealing device on a shaft journal of a dry-running helical rotary compressor

ABSTRACT

A sealing arrangement on a rotor shaft peg of a dry-running rotation screw compressor for establishing a seal between the rotor ( 1 ) and the oil-lubricating bearing ( 7 ) of the shaft peg ( 3 ) has a labyrinth slit seal ( 11 ), located closer to the rotor, and a lip seal ring ( 13 ), located closer to the bearing, and in between an annular space ( 27 ) with ventilation opening ( 29 ) towards the bottom. The shaft peg bears a bearing race ( 25 ) made of a hardened material, which acts in cooperation with the lip sealing ring ( 13 ), and which can also extend above the area of the labyrinth slit seal ( 11 ).

In dry-running rotation screw compressors, no oil for lubrication,cooling and sealing is introduced between the rotors into the sealingspace. The ribs of the main runner and the nuts of the secondary runnerform a “dry” engagement which nevertheless achieves a seal between them.Such screw compressors are particularly suited because they allow theabsence of oil in the seal space in applications in pneumatic conveyorinstallations, for example, for filling and emptying silos, tanks,tanker vehicles and similar instruments with bulk goods. In particular,in the pneumatic conveyance of sensitive goods such as foods orchemicals it is important that the conveyance air stream is free, to ahigh extent, of oil particles.

In the case of dry-running screw rotors, an appropriate seal of theshaft peg must be used to prevent oil from the oil-lubricated bearingsof the shaft pegs to reach the sealing space as a result of leakagealong the shaft pegs. It is already known from GB A 1189856, to arrangeon the shaft peg of rotation screw compressor, next to each other, aconventional sealing ring and an oil sealing ring, which are separatedfrom each other by an annular space which is connected to the externalair. However, because of the high level of abrasion, ordinary sealingrings are unsuited for establishing seals of rapidly rotating shaftpegs, which can reach circumferential speeds of 55-150 m/sec. On theother hand, it is known to use two adjacent, contact-free, labyrinthseals to seal the shaft peg of a dry-running rotation screw compressor;of the labyrinth seals, the one located closest to the oil-lubricatedbearing is in the form of an oil return threading. However, it has beenshown that such contact-free labyrinth seals cannot always reliablyprevent the leakage of oil along the shaft peg to the seal space,particularly if there is high pressure differential on the suction-sideof the seal. From DE A 24 41 520, a shaft seal is known for a screwrotor seal with water injection, which presents several sealing hoopssurrounding the rotor pegs, and located between the annular chambers, ofwhich one is applied to the ring chamber with the gas densified by thecompressor, as a barrier gas, and the other ring chamber is a drainagechamber for bearing oil drainage. The sealing hoops are labyrinth sealhoops, of which one also can be a contact seal. This shaft seal is adynamic seal, which uses pressurized barrier gas, which must be shuntedfrom the conveyor gas stream of the compressor, and which thus entailsan output loss.

It is an object of the invention to provide a sealing arrangement whichworks without barrier gas, which presents a particularly high sealingeffect and, nevertheless, good abrasion resistance, for a shaft peg of adry-running rotation screw compressor.

For achieving the object, the invention provides a sealing arrangementon a rotor shaft peg of a dry-running rotary screw compressor forestablishing a seal between the rotor and an oil-lubricated bearing ofthe shaft peg. The sealing arrangement has a labyrinth gap seal closerto the rotor and a lip seal ring closer to the bearing and in between anannular space with a ventilation opening towards the atmosphere. Theshaft peg carries a bearing ring made of hardened material whichcooperates with the lip sealing ring.

One embodiment variant of the invention is explained in further detailwith reference to the drawing in which:

FIG. 1 is an axial section of an embodiment variant of a sealingarrangement according to invention on a shaft peg of the main runner ofa screw compressor;

FIG. 2 is a section, at an enlarged scale, through a lip seal ring, aspreferably used for the sealing arrangement according to the invention;and

FIG. 3 is a modified embodiment variant of the sealing arrangement.

FIG. 1 is a portion of an axial section through a screw compressor, andit shows diagrammatically one of the rotors, for example, the mainrunner (rib rotor) 1, whose shaft peg 3 is located in a bearing inhousing 5, namely the roller bearing 7. The roller bearing 7 is oillubricated, preferably by means of a lubrication installation (notshown) which produces an oil mist.

A housing ring 9, which is rigidly connected to the housing, is insertedin the housing 5. In the section of the housing ring 1 located closer tothe rotor 1, a labyrinth slit seal 11 in the form of several adjacentring ribs is adapted to its internal circumferential surface. Thislabyrinth slit seal acts contact-free together with the cylindricalcircumferential surface of the section 3 a of the shaft peg 3 to achievethe gas seal.

A lip seal ring 13 is inserted in the housing ring 9 at the section ofthe housing ring 9 located closer to the roller bearing 7; it isrepresented in greater detail in FIG. 2.

The lip seal ring 13 represented in FIG. 2 consists of an externalholder ring 15 and an internal holder ring 17, between which two liprings 19, 21 and a flat seal 23 consisting of flexible elastomermaterials are inserted with tension. The sealing lips 19 a, 21 a of thetwo lip rings 19, 21 have different lengths. The sealing lip 19 a of thelip ring 19, which is bent into the direction of the bearing 7, islonger than the sealing lip 21 a of the sealing ring 21, which is bentin the direction towards the rotor.

In the area of the lip seal ring 13, a bearing race 25 is attached on asection 3 b of the shaft peg 3; preferably it is attached by shrinkage.The bearing race 25, which can be, for example, a conventionalcommercial bearing race for a roller bearing, is made of steel withspecially hardened circumferential surface, to which the lips 19 a and21 a of the lip seal ring 13 are applied. The external diameter of thebearing race 25 is smaller than the external diameter of section 3 a ofthe shaft peg which works in cooperation with the labyrinth slit seal11.

The hardened and extremely precisely machined, for example, polished,external surface of the bearing race 25 produces a particularlyabrasion-reducing application surface for the sealing lips of the lipsealing ring 13. The lip rings 19, 21 are preferably made of anelastomer material based on fluorocarbon polymers.

In the housing ring 9, between the labyrinth slit seal 11 and the lipseal ring 13, a circumferential ring space 27 is formed, which isconnected, through an opening 29 of the housing ring 9, with a space 31of the housing 5, which is open to the atmosphere.

Between the bearing 7 and the lip seal ring 13, on the shaft peg 3 isattached a ring 33 with an external flange, which forms a spray shield,which prevents the direct entry of oil droplets sprayed into the bearing7 toward the lip seal ring 13.

During the operation of the screw compressor, the labyrinth slit seal 11works in the conventional manner as a gas seal, whereas the lip sealring 13 functions as an oil seal with particularly high sealing effect,where leakage from oil from the bearing 7 past the lip seal ring 13 inthe direction of the labyrinth slit seal 11 is prevented with highreliability. The step located in the area of the ring space 27 of thehousing ring 9 between the external surface of the bearing race 25 andthe external surface of the section 3 a of the shaft peg prevents thecreep of oil along the surface. Any volatile components of the oil,which reach the area of the ring space 27, escape through theventilation opening 29 into the external air.

In the embodiment variant represented in FIG. 3, the shaft peg 3 of thedry-running rotor 1 of a screw compressor is placed in a bearing in thehousing 5 by means of oil- or fat-lubricated roller bearings 7 in thehousing 5. A second rotor, which engages in a known manner with rotor 1,is indicated by the reference numeral 2.

As in the embodiment variant according to FIG. 1, in the housing 5, alip seal ring 13 adjacent to the roller bearing 7 and a labyrinth sealring 11 adjacent to the rotor 1 are inserted. In between, there is aring space 27, which is in connection, through a ventilation opening 29with the ventilation duct 31 of the housing, and through it with theexternal air.

On the shaft peg 3, bearing race 25 is attached, for example, byshrinkage, which has an axial length such that it works in cooperation,not only with the lip seal ring 13, but also extends over the area ofthe labyrinth seal ring 11. The specially hardened and polished bearingrace 25 in the preceding embodiment variant normally does not come incontact with the lip seal ring 11. However, should, a contactnevertheless be established between the lip seal ring 11 and the bearingrace 25 as a result of an operational disturbance, then the shaft peg 3is not damaged as a result, only the bearing race 25 is damaged. Thus,by simply replacing the bearing race 25, the correct sealing state canbe reestablished. In addition, the extended bearing race according toFIG. 3 also has the advantage that it can be used as a spacer betweenthe front surface 1 a of the rotor 1 and the roller bearings 7. It isonly then that it becomes possible, by an exact measurement of the axiallength of the bearing race 25, to achieve simultaneously a very precisesetting of the front-side slit between the front surface 1 a of therotor 1 and the corresponding front surface of the housing 5.

What is claimed is:
 1. A rotary screw compressor having a rotor and atleast one rotor shaft peg supported by an oil-lubricated bearing, thecompressor further including a sealing arrangement along the rotor shaftpeg for establishing a seal between the rotor and the oil-lubricatedbearing, the sealing arrangement comprising a housing ring surroundingthe shaft peg, in the portion of the housing ring located closer to therotor, the housing ring including a labyrinth gap seal, which surroundsthe shaft peg; in the portion of the housing ring located closer to theoil-lubricated bearing, the housing ring bears a lip seal ring, and inbetween the lip seal ring and the labyrinth seal, the housing ringdefines a ring space with ventilation opening towards the atmosphere,and in that the shaft peg presents a cylindrical circumferentialsurface, opposite the labyrinth gap seal (11), the sealing arrangementfurther including a bearing race made of hardened material, which isattached to a shaft peg and works in cooperation with the lip seal ring.2. The rotary screw compressor as claimed in claim 1 wherein the bearingrace has an external diameter that is smaller than the circumferentialsurface of the shaft peg, opposite the labyrinth gap seal.
 3. The rotaryscrew compressor as claimed in claim 1 wherein the bearing race alsoforms the circumferential surface of the shaft peg, opposite thelabyrinth gap seal.
 4. The rotary screw compressor as claimed in claim 1wherein the lip seal ring of the sealing arrangement includes thebearing race and first and second sealing lips, which are bent inopposite directions, and applied to the bearing race, the first sealinglip being directed towards the oil-lubricated bearing.
 5. The rotaryscrew compressor as claimed in claim 4 wherein a ring-shaped sprayshield is located between the oil-lubricated bearing and the lip ringseal.
 6. The rotary screw compressor as claimed in claim 4 wherein thebearing race has an external diameter that is smaller than thecircumferential surface of the shaft peg, opposite the labyrinth gapseal.
 7. The rotary screw compressor as claimed in claim 4 wherein thebearing race also forms the circumferential surface of the shaft peg,opposite the labyrinth gap seal.
 8. The rotary screw compressor asclaimed in claim 1 wherein a ring-shaped spray shield is located betweenthe oil-lubricated bearing and the lip seal ring.
 9. The rotary screwcompressor as claimed in claim 8 wherein the bearing race has anexternal diameter that is smaller than the circumferential surface ofthe shaft peg, opposite the labyrinth gap seal.
 10. The rotary screwcompressor as claimed in claim 8 wherein the bearing race also forms thecircumferential surface of the shaft peg, opposite the labyrinth gapseal.